Job seekers will have the opportunity to chat one-on-one with recruiters and hiring managers from companies including Alcoa, Verizon, PNC Financial Services Group Inc., Bank of New York Mellon Corp., United States Steel Corp., UPMC, Highmark and Giant Eagle, the nonprofit said. Vibrant Pittsburgh is hosting a diversity online career fair Tuesday to help job seekers fill an estimated 20,000 open jobs in the region.